1. Field of the Invention
The present invention relates to a method of forming a semiconductor thin film suitable for manufacturing a TFT (Thin Film Transistor) substrate used in, for example, a liquid crystal display or an organic EL (ElectroLuminescence) display, and an inspection apparatus for such a semiconductor thin film.
2. Description of the Related Art
In an active matrix liquid crystal display or an organic EL display using an organic EL device, a TFT substrate is used. The TFT substrate is formed by forming a an amorphous semiconductor thin film or a polycrystalline semiconductor thin film with a relatively small particle diameter on a substrate, and forming a TFT as a drive element through the use of a semiconductor thin film crystal grown by annealing the amorphous semiconductor thin film or the polycrystalline semiconductor thin film by irradiation with a laser beam.
As a light source of an annealing apparatus using a laser beam, an excimer laser having high absorptance into the semiconductor thin film and obtaining a large pulsed light output has been hitherto used. However, since the excimer laser is a gas laser, pulses vary in output intensity. Therefore, TFTs formed through the use of the excimer laser vary in characteristics, thereby to easily cause display unevenness in a display using the TFTs.
Therefore, to prevent a decline in image quality due to variations in pulse intensity in the gas laser, an annealing apparatus using a laser diode with high output stability as a light source has been proposed as described in, for example, Japanese Unexamined Patent Application Publication No. 2003-332235. However, a light output obtained from the laser diode is very small, compared to that from the excimer laser or the like, so the size of a beam in an annealing process is also small. Therefore, an annealing process time per unit area of the TFT substrate is increased, thereby to cause a decline in productivity or an increase in manufacturing cost.
Thus, for the purpose of achieving a higher throughput in the annealing process, there is proposed an annealing method in which a plurality of laser light sources are arranged in proximity to one another and a plurality of laser beams from the plurality of laser light sources are simultaneously applied to a plurality of regions on an amorphous semiconductor thin film, thereby to reduce a scanning time and improve productivity as described in, for example, Japanese Unexamined Patent Application Publication No. 2004-153150.
On the other hand, a method of controlling crystallization of a semiconductor thin film through the use of such a laser diode has been performed by a laser beam intensity monitoring means included in an annealing apparatus. For example, in a method of monitoring laser beam intensity described in, for example, Japanese Unexamined Patent Application Publication No. 2005-101202, a single intensity measurement section is used for optical paths of a plurality of laser optical systems, so one intensity measurement section is moved over the optical paths of the laser optical systems so as to sense light on each of the optical paths, thereby the irradiation energy of each of the plurality of laser optical systems is measurable by one intensity measurement section.
Moreover, for example, Japanese Unexamined Patent Application Publication No. 2002-319606 discloses a method of evaluating the degree of crystallization in an annealed region (crystallized region) by determining a high level and a low level of luminance based on irradiation light in the annealed region. More specifically, the degree of crystallization is evaluated on the basis of a state of high crystallinity and low crystallinity in the crystallized region.